Antioxidant aromatic diphosphites

ABSTRACT

An aromatic diphosphite as a antioxidant for organic materials. The aromatic diphosphite has the formula: ##STR1## wherein each R is independently selected from the group consisting of hydrogen and methyl; and R 1 , R 2  and R 3  are each independently selected from the group consisting of hydrogen and straight chain and branched alkyl groups having from 1 to about 18 carbon atoms with the proviso that at least two of said R 1 , R 2 , and R 3  are alkyl groups having at least three carbon atoms.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to hydrolytically stable aromatic diphosphitesand their use as antioxidants in organic materials such as organicpolymers.

2. Description of the Prior Art

Phosphites are used in organic polymers and other organic materials asantioxidants. The phosphites are generally considered better thanphenolic antioxidants at high temperatures because they eliminatehydroperoxides which decompose and lead to autooxidation chainreactions. Thus, phosphites are important for oxidative stability duringvarious operations including polyolefin extrusion.

Phenolic and phosphite antioxidants are often used together inpolyolefin homopolymers and copolymers to provide antioxidant protectionfor both low and high temperature exposure. Unfortunately, additionalexpense is encountered as additives in larger amounts are needed for thepolymers. Thus, there exists a need for effective antioxidants at areasonable additive price, not only for polyolefins, but othersubstrates as well.

It is common practice to include an antioxidant in organic materialsnormally susceptible to oxidative degradation. Many of the antioxidantsemployed have limited effectiveness or tend to impart undesirableproperties to the organic material such as causing color. The problem isparticularly acute with polymers and copolymers of ethylenicallyunsaturated monomers, especially polyolefins such as polypropylene.These materials are subjected to elevated temperatures duringprocessing, which tends to destroy many antioxidants with the resultthat the polymer rapidly degenerates during use. The compounds of thepresent invention allow organic materials to maintain excellent colorand thermal stability.

SUMMARY OF THE INVENTION

According to the present invention, certain aromatic diphosphites areprovided which are very effective as stabilizers in a wide range oforganic materials. The aromatic diphosphites are very effective becausethey retard changes in viscosity of organic materials stabilizedtherewith for extensive periods of time under oxidative conditions. Inaddition, they are stable when stored at room temperatures. They areespecially effective when used in combination with phenolicantioxidants.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The aromatic diphosphites of the present invention are particularlyuseful as an antioxidant for an organic material normally susceptible todegradation in the presence of oxygen by including in the organicmaterial an antioxidant amount of the aromatic diphosphites.

The aromatic diphosphites of the present invention are represented bythe formula: ##STR2## wherein each R is independently selected from thegroup consisting of hydrogen and methyl; and R¹, R² and R³ are eachindependently selected from the group consisting of hydrogen andstraight chain and branched alkyl groups having from 1 to about 18carbon atoms with the proviso that at least two of said R¹, R² and R³groups are alkyl groups having at least three carbon atoms.

Examples of R¹, R², and R³ include hydrogen and alkyl groups such asmethyl, ethyl, propyl, isopropyl, butyl, sec-butyl, isobutyl,tert-butyl, pentyl, isopentyl, tert-pentyl, isohexyl, 3-methylpentyl,2,3-dimethylbutyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl,tetradecyl, hexadecyl, octadecyl and the like.

It is particularly preferred that R¹ and R² be tertiary alkyl groupscontaining 4 to about 18 carbon atoms such as tertiary butyl, tertiarypentyl, tertiary hexyl, tertiary heptyl, and the like, and morepreferably that R¹ and R² be tertiary butyl groups.

The preferred aromatic diphosphite of the present invention istetrakis(2,4-di-tert-butylphenyl) 4,4'-isopropylidenediphenyldiphosphite and is represented by the formula: ##STR3##

The aromatic diphosphites of the invention are particularly useful asantioxidants. The antioxidants can be used in a broad range of organicmaterial normally subject to gradual degradation in the presence ofoxygen during use over an extended period. In other words, the organicmaterials protected by the present antioxidants are of the type in whichthe art recognizes the need for antioxidant protection and to which anantioxidant of some type is customarily added to obtain an extendedservice life. The oxidative degradation protected against is the slowgradual deterioration of the organic composition rather than, forexample, combustion.

Examples of organic materials in which the antioxidants are usefulinclude polymers, both homopolymers and copolymers, of olefinicallyunsaturated monomers, for example, polyolefins such as polyethylene,polypropylene, polybutylene, and the like.

Also, polyhalohydrocarbons such as polyvinyl chloride, polychloroprene,polyvinylidene chloride, polyfluoroolefins, and the like, are affordedstabilization. The antioxidants provide antioxidant protection innatural and synthetic rubbers such as copolymers of olefinicallyunsaturated monomers including styrene-butadiene rubber (SBR rubber),ethylene-propylene copolymers, ethylene-propylene-diene terpolymers suchas the terpolymer of ethylene, propylene and cyclopentadiene or1,4-cyclooctadiene. Polybutadiene rubbers such as cis-polybutadienerubber are protected. Poly-2-chloro-1,3-butadiene (neoprene) andpoly-2-methyl-1,3-butadiene (isoprene rubber) are stabilized by thepresent additives. Likewise, acrylonitrile-butadiene-styrene (ABS)resins are effectively stabilized. Ethylene-vinyl acetate copolymers areprotected, as are butene-methylacrylate copolymers. Nitrogen-containingpolymers such as polyurethanes, nitrile rubber, and laurylacrylate-vinyl pyrrolidone copolymers are effectively stabilized.Adhesive compositions such as solutions of polychloroprene (neoprene) intoluene are protected.

Petroleum oils such as solvent-refined, midcontinent lubricating oil andGulf Coast lubricating oils are effectively stabilized. In hydrocarbonlubricating oils, both mineral and synthetic, the present antioxidantsare particularly effective when used in combination with a zincdihydrocarbyl dithiophosphate e.g. zinc dialkyl dithiophosphate or zincdialkaryl dithiophosphate.

Synthetic ester lubricants such as those used in turbines and turbojetengines are given a high degree of stabilization. Typical syntheticester lubricants include di-2-ethylhexyl sebacate, trimethylolpropanetripelargonate, C₅₋₉ aliphatic monocarboxylic esters of pentaerythritol,complex esters formed by condensing under esterifying conditions,mixtures of polyols, polycarboxylic acids, and aliphatic monocarboxylicacids and/or monohydric alkanols. An example of these complex esters isthe condensation product formed from adipic acid, ethylene glycol and amixture of C₅₋₉ aliphatic monocarboxylic acids. Plasticizers such asdioctyl phthalate are effectively protected. Heavy petroleum fractionssuch as tar and asphalt can also be protected should the need arise.

Polyamides such as adipic acid-1-6-diaminohexane condensates andpoly-6-aminohexanoic acid (nylon) are effectively stabilized.Polyalkylene oxides such as copolymers of phenol with ethylene oxide orpropylene oxide are stabilized. Polyphenyl ethers such aspoly-2,6-dimethylphenyl ether formed by polymerization of2,6-dimethylphenol using a copper-pyridine catalyst are stabilized.Polycarbonate plastics and polyformaldehydes are also protected.

Linear polyesters such as phthalic anhydride-glycol condensates aregiven a high degree of protection. Other polyesters such as trimelliticacid-glycerol condensates are also protected. Polyacrylates such aspolymethylacrylate and polymethylmethacrylate are effectivelystabilized. Polyacrylonitriles and copolymers of acrylonitriles withother olefinically unsaturated monomers such as methylmethacrylates arealso effectively stabilized.

The antioxidants of the present invention are preferably used in eitherthermoset or thermoplastic polymer compositions. The thermoset polymersare those plastics which when subjected to heat, will normally becomeinfusible or insoluble and as such cannot be remelted. They haveelaborately cross-linked three dimensional structures and are used forplastics, elastomers, coatings and adhesives.

In contrast to the thermoset polymers, most thermoplastic polymers canbe made to soften and take a new shape by the application of heat andpressure. Thermoplastic polymers comprise long-chain molecules oftenwithout any branching (e.g., high density polyethylene). Thermoplasticpolymers normally are rigid at operating temperatures, but can beremelted and reprocessed. They include polyethylene, polycarbonate,polypropylene, polystyrene, polyvinyl chloride,acrylonitrile-butadiene-styrene (ABS), nylon, and the like, includingpolymers intended for high temperature applications. The most preferredorganic compounds intended for the practice of the present invention arepolypropylene and polyethylene.

The antioxidants are incorporated into the organic material in a smallbut effective amount so as to provide the required antioxidantprotection. A useful range is generally from about 0.005 to about 5weight percent of organic material, and a preferred range is from about0.02 to 2 weight percent.

Methods of incorporating the antioxidants into the organic material arewell known. For example, if the material is liquid, the additive can bemerely mixed into the material. Solid organic materials can be merelysprayed with a solution of the additive in a volatile solvent. Forexample, stabilized grain products result from spraying the grain with atoluene solution of the antioxidant. In the case of rubbery polymers,the additive can be added following the polymerization stage by mixingit with the final emulsion or solution polymerization mixture and thencoagulating or removing solvent to recover the stabilized polymer. Itcan also be added at the compounding stage by merely mixing the additivewith the rubbery polymer in commercial mixing equipment such as aBanbury blender. In this manner, rubbery polymers such asstyrene-butadiene rubber, cis-polybutadiene or isoprene polymers areblended with the antioxidant together with the other ingredientsnormally added such as carbon black, oil, sulfur, zinc oxide, stearicacid, vulcanization accelerators, and the like. Following mastication,the resultant mixture is fabricated and molded into a finished form andvulcanized.

The aromatic diphosphites of the present invention can be prepared byreacting a 2,4- or 2,6-dialkylphenol or a 2,4,6-trialkylphenol and aphosphorus trihalide such as PCl₃ or PBr₃ in the presence of an aproticsolvent, such as tetrahydrofuran, aromatic solvents such as benzene andtoluene or aliphatic solvents such as heptane, octane, and nonane andgenerally at a temperature greater than the melting point of the solventbut less than the boiling point of the solvent to form an intermediatediaryl halophosphite and subsequently reacting the intermediate with anappropriate 4,4'-bisphenol alkane, such as 4,4'-isopropylidenebisphenol(bisphenol A), to produce the aromatic diphosphite. The intermediatediaryl halophosphite may be isolated and purified prior to its reactionwith bisphenol A or may be reacted with the bisphenol A in a one stepprocess.

The preferred temperature used in the preparation of the aromaticdiphosphite product is generally in the range of from about -10° C. toabout 300° C. Preferably, the temperature is within the range from about5° C. to about 150° C.

The preparation of the intermediate diaryl halophosphite is preferablycarried out by adding the dialkylphenol or trialkylphenol to the aproticsolvent containing the phosphorus trihalide at a temperature sufficientto form the intermediate. The preferred mole ratio of phosphorustrihalide to dialkylphenol or trialkylphenol used to form thesubstituted diaryl halophosphite is preferably 0.9-1.1:1.9-2.1.

The second step of the reaction is carried out by mixing the substituteddiaryl halophosphite from the first step of the reaction with theappropriate 4,4'-bisphenol alkane, preferably at a mole ratio of about1.9-2.1:1, in the aprotic solvent at a sufficient reaction temperature.

The preferred reaction conditions include a pressure high enough toallow the reaction to proceed at a reasonable rate yet not so high as toadversely affect the course of the reaction. The reaction is generallyrun at atmospheric pressure.

No particular type of atmosphere is required. However, a nitrogenatmosphere is generally preferred since it is a common way of keepingoxygen and moisture out of the reaction system.

The alkylated phenol used in preparing the aromatic diphosphites has theformula: ##STR4## wherein R¹, R², and R³ are each independently selectedfrom the group consisting of hydrogen and straight chain and branchedalkyl groups having from about 1 to about 18 carbon atoms with theproviso that at least two of said R¹, R² and R³ groups are alkyl groupshaving at least three carbon atoms.

Examples of alkyl groups include: methyl, ethyl, propyl, isopropyl,butyl, sec-butyl, isobutyl, tert-butyl, pentyl, isopentyl, tert-pentyl,isohexyl, 3-methylpentyl, 2,3-dimethylbutyl, heptyl, octyl, nonyl,decyl, undecyl, dodecyl, tetradecyl, hexadecyl, octadecyl, and the like.

The aromatic diphosphites of the present invention may be used alone asthe antioxidant or may be used in combination with phenolicantioxidants, light stabilizers such as hindered amines or ultravioletlight absorbers, metal deactivators, pigments, dyes, lubricants such ascalcium stearate, nucleation agents, and talc and other fillers.

Phenolic antioxidants which are suitable for use in the presentinvention are well known in the art and include2,6-di-t-butyl-4-methylphenol, 2,6,-di-t-butyl-4-methoxymethylphenol,2,6-dioctadecyl-4-methylphenol, 3,5-di-t-butyl-4-hydroxyanisole,2,5-di-t-butyl-4-hydroxyanisole, 4-(hydroxymethyl)-2,6-di-t-butylphenol,4,4'-methylenebis(2,6-di-t-butylphenol),2,2'-ethylidenebis(4,6-di-t-butylphenol),4,4'-thiobis(2-methyl-6-t-butylphenol), tetrakis(methylene3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate)methane,1,3,5-tris(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate,O,O'-di-n-octadecyl(3,5-di-t-butyl-4-hydroxybenzyl)phosphonate,octadecyl 3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate,2,2'-oxamidobisethyl 3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate,calcium bis(O-ethyl(3,5-di-t-butyl-4-hydroxybenzyl)phosphonate) andmixtures thereof. A particularly preferred phenolic antioxidant is1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene whichis available from Ethyl Corporation as Ethanox® 330 antioxidant.

When utilized, the phenolic antioxidants are preferably present with thearomatic diphosphites in an amount in the range of from about 0.005 toabout 3.0 percent by weight based on the weight of the totalcomposition.

The following examples are presented to illustrate certain specificembodiments of the invention, but are not intended to be construed so asto be restrictive of the spirit and scope thereof.

EXAMPLE 1

Preparation of Tetrakis(2,4-di-tert-butylphenyl)4,4'-isopropylidenediphenyl diphosphite

Under a nitrogen atmosphere, 2.15 g of bisphenol A and 2.8 ml oftriethylamine were added to a 50 ml flask. A solution of 10.6 g of 90%bis(2,4-di-tert-butylphenyl) chlorophosphite in 20 ml of anhydroustetrahydrofuran was added to the flask. The mixture was heated to refluxtemperature and maintained at that temperature for about 1 hour. Theresulting slurry was allowed to cool and then filtered throughdiatomaceous earth. The solids were washed with n-heptane. The collectedfiltrate was concentrated under vacuum to 9.6 g of a pure yellow oil.The oil was purified by chromatography on silica gel to yield a whitesolid. The resulting solid had a melting point of 58° C. The P-NMRrevealed a singlet with a chemical shift of 129 ppm (δ from H₃ PO₄). TheIR and H-NMR were consistent with the assigned structure oftetrakis(2,4-di-tert-butylphenyl) 4,4'-isopropylidenediphenyldiphosphite.

EXAMPLE 2

In order to demonstrate the effectiveness of the aromatic diphosphitesof the present invention as processing stabilizers,tetrakis(2,4-di-tert-butylphenyl) 4,4'-isopropylidenediphenyldiphosphite (hereinafter referred to as "Phos.A") and1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene(Ethanox® 330 antioxidant) were incorporated into polypropylene powderin accordance with the following procedure. The Phos.A and Ethanox 330antioxidant were dissolved in a small amount of methylene chloride andmixed with 50 g of polypropylene powder (Profax 6501 from Hercules). Themixture was then dry blended with 450 g of polypropylene in a nitrogenatmosphere. In all formulations, 1000 ppm of calcium stearate(Mallinckrodt RSN 248D) was utilized as an acid neutralizer andlubricating agent. The blended material were extruded under nitrogen ona twin screw mixer (Brabender, 30 rpm) with the following temperatureprofile: zone one--150° C., zone two and zone three--245° C. Then,multiple extrusions were run on the pellets on a single screw extruder(Brabender L/D 24:1) at 500° F. The stock temperature was 265° C. andthe screw speed was 30 rpm in an air atmosphere. The extruded strand wascooled by passing it through a room temperature (24°-29° C.) water bath.Water carryover was minimized by an air knife that blew the excess waterfrom the strand before it entered the pelletizer. The melt flow index(MFI) was determined with a Tinium Olsen Extrusion Plastometer accordingto ASTM Method D-1238 Condition L (230° C.-2160 g load). Using the samesamples, a 60 mil sheet was pressed out at 375° F. and the color wasdetermined with a Hunterlab Optical Sensor Model D25.

The results of these tests are shown in Table I.

                  TABLE I                                                         ______________________________________                                                        Melt Flow Yellowness                                                          Index Extrusion                                                                         Index Extru-                                                        Pass No.  sion Pass No.                                       Test No.                                                                             Antioxidant                                                                              Wt. %   1   3    5    1   3   5                             ______________________________________                                        1      None       --      5.0 13.9 --   5.0 7.2 --                            2      Ethanox 330                                                                              0.05    3.2 6.2  9.8  4.6 --  7.4                           3      Phos. A    0.05    2.0 3.1  4.0  4.5 --  6.6                                  Ethanox 330                                                                              0.05                                                        ______________________________________                                    

The results of these tests demonstrate that Phos.A was effective inreducing the degradation of polypropylene and suppressing the formationof color when used with Ethanox 330 antioxidant.

EXAMPLE 3

A series of tests were performed in the same manner as Example 2 exceptthat a different batch of Profax 6501 polypropylene was used, no calciumstearate was added, and the extrusions were carried out at 550° F.

The results of these tests are shown in Table II.

                  TABLE II                                                        ______________________________________                                                        Melt Flow Yellowness                                                          Index Extrusion                                                                         Index Extru-                                                        Pass No.  sion Pass No.                                       Test No.                                                                             Antioxidant                                                                              Wt. %   1   2    3    1   2   3                             ______________________________________                                        1      None       --      9.3 19.2 --   6.5 8.5 --                            2      Ethanox 330                                                                              0.05    6.7 9.4  12.6 7.2 --  9.6                           3      Phos. A    0.05    6.4 8.4  11.8 6.1 --  8.5                                  Ethanox 330                                                                              0.05                                                        ______________________________________                                    

These results of these tests demonstrate that Phos.A was effective inreducing the degradation of polypropylene and suppressing the formationof color when used with Ethanox 330 antioxidant.

EXAMPLE 4

A series of tests were performed in the same manner as Example 2 exceptthat a different batch of Profax 6501 polypropylene was used, and theextrusions were carried out at 550° F.

The results of these tests are shown in Table III.

                  TABLE III                                                       ______________________________________                                                         Melt Flow Index                                                                            Yellowness                                                       Extrusion    Index Extru-                                                Wt.  Pass No.     sion Pass No.                                   Test No.                                                                             Antioxidant                                                                              %      1    2    3    1   2   3                             ______________________________________                                        1      None       --     13.8 26.9 --   5.0 6.2 --                            2      Ethanox 330                                                                              0.05   8.9  13.2 18.8 4.5 --  6.1                           3      Phos. A    0.05   5.7   7.4 10.5 4.7 --  6.3                                  Ethanox 330                                                                              0.05                                                        ______________________________________                                    

The results of these tests demonstrate that Phos.A was effective inreducing the degradation of polypropylene when used with Ethanox 330antioxidant.

EXAMPLE 5

Tests were carried out by first dissolving or dispersing either2,2'-ethylidenebis(4,6-di-t-butylphenol) (a phenolic antioxidant whichis available from Ethyl Corporation as Ethanox® 308 antioxidant) or amixture of Ethanox® 308 antioxidant and Phos.A in a small amount ofmethylene chloride and mixed with 50 g of high density polyethylene(Soltex® XF-397 which is available from Solvey et Cie). The mixtureswere then dry blended with 450 g of high density polyethylene undernitrogen. The blended materials were pelletized under nitrogen on a twinscrew mixer (Brabender) with the following profile: zone one--150° C.,zones two and three--200° C.; stock temperature--204°-206° C.; screwspeed 30 rpm. Then, multiple extrusions (5 passes) were run on thepellets on a single screw extruder (Brabender L/D 24:1) with atemperature profile of the following: zones one and two at 218° C., zonethree at 232° C. and zone four at 246° C. The stock temperature was253°-255° C. and the screw speed 30 rpm in an air atmosphere. Theextruded strand was cooled by passing it through a room temperature(24°-29° C.) water bath. Water carryover was minimized by an air knifethat blew the excess water from the strand before it entered thepelletizer. Material from each pass was collected and 60 mil sheets werepressed out at 375° F., and color was determined with a HunterlabOptical Sensor Model D 25.

The results of these tests are shown in Table IV.

                  TABLE IV                                                        ______________________________________                                                           Yellowness Index                                                              Extrusion Pass No.                                         Test No. Antioxidant Wt %    1      3    5                                    ______________________________________                                        1        Ethanox 308 0.05    8.5    12.9 15.0                                 2        Phos. A     0.05    5.9    9.8  12.5                                          Ethanox 308 0.05                                                     3        Ethanox 308 0.10    1.6    3.8   6.9                                          Zinc Stearate                                                                             0.05                                                     4        Ethanox 308 0.10    -0.26  1.8   4.2                                          Phos. A     0.05                                                              Zinc Stearate                                                                             0.05                                                     ______________________________________                                    

The results of these tests show that Phos.A was effective in suppressingthe formation of color when used with Ethanox® 308 antioxidant.

The invention is not limited to the above-described specific embodimentsthereof; it must be understood, therefore, that the detail involved inthe descriptions of the specific embodiments is presented for thepurpose of illustration only, and that reasonable variations, which willbe apparent to those skilled in the art, can be made in this inventionwithout departing from the spirit and scope thereof.

We claim:
 1. An antioxidant composition comprisingtetrakis(2,4-di-tert-butylphenyl) 4,4'-isopropylidenediphenyldiphosphite and1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl) benzene.2. Polyolefin containing the antioxidant composition of claim
 1. 3. Acomposition of claim 2 wherein said polyolefin is a polypropylene.
 4. Acomposition of claim 3 further defined by containing calcium stearate.5. An antioxidant composition comprisingtetrakis(2,4-di-tert-butylphenyl) 4,4'-isopropylidenediphenyldiphosphite and 2,2'-ethylidenebis(4,6-di-tert-butylphenol). 6.Polyolefin containing the antioxidant composition of claim
 5. 7. Acomposition of claim 6 wherein said polyolefin is polyethylene.
 8. Acomposition of claim 7 further defined by containing zinc stearate.
 9. Aphosphite stabilizer for organic compositions said stabilizer beingtetrakis(2,4-di-tert-butylphenyl) 4,4'-isopropylidenediphenyldiphosphite.